1. Field of the Invention
The present invention relates to a printer in which two sets of rollers are maintained in pressure contact with a sheet advancing roller such as a platen roller.
2. Description of the Prior Art
In conventional printers such as a typewriter, two sets of pinch rollers are maintained in contact with a platen roller functioning as a sheet advancing roller. FIGS. 1 and 2 represent a conventional example, in which a printing head 1 mounted on a carriage 2 moves in a direction perpendicular to the plane of the drawing (in FIG. 1) along guide rails 3, 4. In front of the printing head 1 there is provided a platen 5, and a sheet holding roller 6 and a pinch roller 7 are maintained, in separable manner, in contact with the platen 5. A sheet guide 8 introduces a printing sheet 9, introduced from a direction A, between the platen 5 and the pinch roller 7, and the sheet is further guided between the printing head 1 and the platen 5 by rotation thereof in a direction B. The sheet holding roller 6 is at first retracted to position 6' shown in broken line and is brought to position 6 shown in solid line in contact with the platen 5 after the leading end of the printing sheet has passed between the roller 6 and the platen 5. In such a structure, however, at the loading of the printing sheet, the operator is required to perform the cumbersome operation of manually separating the sheet holding roller as shown in FIG. 2 and again bringing the roller in contact with the platen 5 after it is rotated.
This printer can also use a fan-fold printing sheet 10 provided with perforations along both sides. The perforations of such a fan-fold sheet 10 are at first fitted on pins 11a of a tractor 11, and the leading end of the sheet is then wound around the platen 5, by moving the sheet holding roller 6 to the position 6', then advancing the fan-fold sheet 10 by means of the platen 5 and the pinch roller 7 and returning the sheet holding roller 6 to position 6 after the leading end of the sheet has passed between the sheet holding roller and the platen, thereby supporting the fan-fold sheet 10 between the roller 6 and the platen 5. Thereafter a lever 12 is actuated to separate the pinch roller 7 from the platen, enabling the printing operation. In this manner the loading of the fan-fold sheet is also quite cumbersome.